Central vs peripheral nerve conduction. Before and after treatment of subacute combined degeneration
H. Tomoda, H. Shibasaki, I. Hirata and K. Oda
Department of Internal Medicine, Saga Medical School, Japan.
Central and peripheral nerve conduction was studied in two patients with
subacute combined degeneration by using the short-latency somatosensory
evoked potentials and the peripheral nerve conduction study during
treatment with cyanocobalamin. Before the treatment, somatosensory evoked
potentials with median nerve stimulation were normal, but those with
peroneal nerve stimulation revealed prolonged central conduction indicating
dysfunction within the posterior column. Peripheral sensory and motor nerve
action potentials were reduced with normal or slightly reduced conduction
velocity. After treatment, marked shortening of the central conduction time
(by 24% and 31%, respectively) was observed with mild or no recovery of
peripheral nerve action potentials. These physiologic findings suggest that
the main pathologic changes in the central nervous system may be
demyelination in the posterior column in addition to axonal degeneration in
the peripheral nerve. The former was responsive to treatment but the latter
was poorly responsive to treatment. Sensory symptom in subacute combined
degeneration appears to be, at least partially, attributed to the spinal
cord lesion.
